[new feature] OverlayImage processor

processor that adds an image over the original image.
Added in overlay.py
test added in test_processor.py

Author: Psylocibus

pilkit/processors/overlay.py

@@ -21,3 +21,30 @@ def process(self, img):
         mask = Image.new('RGBA', original.size, (0,0,0,int((1.0 - self.overlay_opacity)*255)))
         img = Image.composite(original, overlay, mask).convert('RGB')
         return img
+
+
+class ImageOverlay(object):
+    """
+    Overlay an image (i.e watermark) with a given opacity over the original image.
+    """
+
+    def __init__(self, overlay_img, position=(0,0)):
+        """
+        :param overlay_img: PIL `Image` instance to overlay on the original image
+        :param position: coordinate (x,y) of the top left corner of the overlay image on the original image. 
+        """
+        self.overlay_img=overlay_img
+        self.position=position
+        
+    def process(self, img):
+        #create the mask (image of same dimension as the original, with the overlay at the right location, with the given opacity)
+        mask = Image.new("RGBA",(img.width, img.height),(0,0,0,0)) #transparent image with the same dimensions as original image
+        mask.paste(self.overlay_img, (self.position[0], self.position[1])) #put the overlay image at the computed location
+
+        #render the picture overlayed
+        if img.mode != "RGBA" :
+            tmp = Image.alpha_composite(img.convert("RGBA"), mask) #apply the overlay (both images need to be in "RGBA" mode with alpha_composite())
+            img = tmp.convert(img.mode) #convert back to the original mode
+        else :
+            img = Image.alpha_composite(img, mask)
+        return img

tests/assets/ImageOverlay_expected_result.png

@@ -5,7 +5,7 @@
 from pilkit.lib import Image, ImageDraw, ImageColor
 from pilkit.processors import (Resize, ResizeToFill, ResizeToFit, SmartCrop,
                                SmartResize, MakeOpaque, ColorOverlay, Convert,
-                               GaussianBlur)
+                               GaussianBlur, ImageOverlay)
 from pilkit.processors.resize import Thumbnail
 from .utils import create_image, compare_images, get_image_file
 
@@ -56,6 +56,32 @@ def test_coloroverlay():
     img = ColorOverlay(color, overlay_opacity=1.0).process(img)
     assert img.getpixel((0,0)) == (204, 0, 0)
 
+def test_imageoverlay():
+    """
+    Test ImageOverlay processor
+    """
+    #test with RGBA mode background image
+    background_img_rgba = Image.open(get_image_file("reference.png")).convert("RGBA")
+    overlay_img_rgba = Image.open(get_image_file("image_with_transparency.png"))
+    result_1 = background_img_rgba
+    result_1 = ImageOverlay(overlay_img_rgba, (56,156)).process(result_1) #the overlay is completely inside the background image
+    result_1 = ImageOverlay(overlay_img_rgba, (-30,-10)).process(result_1) #the overlay top left corner is in the void
+    result_1 = ImageOverlay(overlay_img_rgba, (199,36)).process(result_1) #the overlay bottom right corner is in the void
+    expected_result_1 = Image.open(get_image_file("ImageOverlay_expected_result.png")).convert("RGBA") #This image have been generated with gimp
+    assert compare_images(result_1, expected_result_1) #overlay are positioned as expected 
+    assert result_1.mode == "RGBA" #the mode of the result is the same as the original 
+
+    #test with RGB mode background image
+    background_img_rgb = Image.open(get_image_file("reference.png")).convert("RGB")
+    result_2 = background_img_rgb
+    result_2 = ImageOverlay(overlay_img_rgba, (56,156)).process(result_2) #the overlay is completely inside the background image
+    result_2 = ImageOverlay(overlay_img_rgba, (-30,-10)).process(result_2) #the overlay top left corner is in the void
+    result_2 = ImageOverlay(overlay_img_rgba, (199,36)).process(result_2) #the overlay bottom right corner is in the void
+    expected_result_2 = Image.open(get_image_file("ImageOverlay_expected_result.png")).convert("RGB") #This image have been generated with gimp
+    assert compare_images(result_2, expected_result_2) #overlay are positioned as expected 
+    assert result_2.mode == "RGB" #the mode of the result is the same as the original
+
+
 def test_convert():
     img = Image.new('RGBA', (200, 100))